The invention relates to a speaker apparatus and, more particularly, to a speaker apparatus having a primary coil and a secondary coil.
Hitherto, an electromagnetic induction speaker has been known. As such a speaker, there are what is called an inner magnetic type electromagnetic induction speaker in which a magnet is arranged inside and what is called an outer magnetic type electromagnetic induction speaker in which a magnet is arranged outside.
As shown in FIG. 1, an inner magnetic type electromagnetic induction speaker 100 has a yoke 110, a magnet 120, and a diaphragm 130.
The yoke 110 is constructed by integratedly forming: a disk-shaped bottom portion 111; a peripheral wall portion 112 projected upward from a peripheral edge of the bottom portion 111; and a ring-shaped annular plate 113 provided at the upper edge of the peripheral wall portion 112. The cylindrical magnet 120 is attached to the center portion of the upper surface of the bottom portion 111. The upper surface of the annular plate 113 of the yoke 110 is attached to a frame 140.
A disk-shaped center plate 150 is attached to the upper surface of the magnet 120. The center plate 150 is arranged in a center hole 113a of the annular plate 113. A gap formed between the annular plate 113 and center plate 150 is a magnetic gap 160.
The diaphragm 130 is constructed by integratedly forming: an almost semispherical dome portion 131 provided in the center portion; and an edge portion 132 having a small arc-shaped cross section and formed so as to be continuous with the outer periphery of the dome portion 131. An outer edge portion of the edge portion 132 is attached to the upper surface of the frame 140. An upper edge of a cylindrical bobbin 170 is fixed to the outer peripheral edge of the dome portion 131 by adhesion or the like.
A secondary coil 171 of one turn is wound around a portion near the lower edge of the bobbin 170 and fixed. The secondary coil 171 is located in the magnetic gap 160 formed between the annular plate 113 and center plate 150.
A primary coil 180 on the outer peripheral side and a primary coil 190 on the inner peripheral side are arranged in the magnetic gap 160 so as to face each other through the secondary coil 171. The outer peripheral side primary coil 180 is fixed to the inner peripheral surface of the annular plate 113 of the yoke 110. The inner peripheral side primary coil 190 is fixed to the outer peripheral surface of the center plate 150. The outer peripheral side primary coil 180 and inner peripheral side primary coil 190 are serially connected. One end of the outer peripheral side primary coil 180 is connected to a signal lead wire 180a. One end of the inner peripheral side primary coil 190 is connected to a signal lead wire 190a. 
When a current based on an audio signal which is supplied from an audio signal reproducing unit (not shown) is supplied to the outer peripheral side primary coil 180 and inner peripheral side primary coil 190, an induction current flows in the secondary coil 171 arranged in the magnetic gap 160. The diaphragm 130 is vibrated by a Lorentz force. The audible sound based on the audio signal corresponding to the current supplied to the primary coil 190 is generated.
As shown in FIG. 2, an outer magnetic type speaker 200 comprises a yoke 210, a magnet 220, and a diaphragm 230.
The yoke 210 is constructed by integratedly forming: a disk-shaped bottom portion 211; and a center pole 212 projected upward from the center portion of the bottom portion 211. The cylindrical magnet 220 is attached to an outer edge portion of the upper surface of the bottom portion 211.
A ring-shaped annular plate 240 is attached to the upper surface of the magnet 220. The annular plate 240 is arranged in correspondence to the upper edge portion of the center pole 212. An upper surface of the outer edge portion of the annular plate 240 is attached to a frame 250. A gap formed between the annular plate 240 and center pole 212 is a magnetic gap 260.
The diaphragm 230 comprises: a center portion 231 having an arc-shaped cross section and locating in the center portion; an inclined portion 232 which is provided so as to be continuous with the outer periphery of the center portion 231 and deviated upward as it approaches the outward position; an edge portion 233 which is continuous with the outer periphery of the inclined portion 232; and a fixing portion 234 which is provided so as to be continuous with the outer periphery of the center portion 231 and is projected in the direction opposite to the inclined portion 232. An outer edge portion of the edge portion 233 is attached to the upper surface of the outer edge portion of the frame 250. An upper edge portion of a cylindrical bobbin 270 is fixed to an edge portion of the fixing portion 234 by adhesion or the like.
A secondary coil 271 of one turn is wound around a portion near the lower edge of the bobbin 270 and fixed. The secondary coil 271 is located in the magnetic gap 260 formed between the annular plate 240 and center pole 212.
A primary coil 280 on the outer peripheral side and a primary coil 290 on the inner peripheral side are arranged in the magnetic gap 260 so as to face each other through the secondary coil 271. The outer peripheral side primary coil 280 is fixed to the inner peripheral surface of the annular plate 240. The inner peripheral side primary coil 290 is fixed to the upper edge portion of the outer peripheral surface of the center pole 212. The outer peripheral side primary coil 280 and inner peripheral side primary coil 290 are serially connected. One end of the outer peripheral side primary coil 280 is connected to a signal lead wire 280a. One end of the inner peripheral side primary coil 290 is connected to a signal lead wire 290a. 
When a current based on an audio signal which is supplied from an audio signal reproducing unit (not shown) is supplied to the outer peripheral side primary coil 280 and inner peripheral side primary coil 290 in a manner similar to the speaker 100 shown in FIG. 1 mentioned above, an induction current flows in the secondary coil 271 arranged in the magnetic gap 260. The diaphragm 230 is vibrated by a Lorentz force. The audible sound based on the audio signal corresponding to the supplied current is generated.
When the primary coils 180, 190, 280, and 290 mentioned above are fixed to the annular plates 113 and 240 or the center plate 150 or center pole 212, there are generally the following two methods.
(1) In a state where the primary coils 180, 190, 280, and 290 are wound and fixed to the outer peripheral surface of the cylindrical bobbin (not shown), they are internally fitted to the annular plates 113 and 240 or externally fitted to the center plate 150 or center pole 212 and fixed by adhesion or the like.
(2) In a state where the primary coils 180, 190, 280, and 290 are wound without using any bobbin (they are formed as bobbinless coils), they are internally fitted to the annular plates 113 and 240 or externally fitted to the center plate 150 or center pole 212 and fixed by adhesion or the like.
Generally, the foregoing bobbins and the primary coils 180, 190, 280, and 290 which are internally fitted to the annular plates 113 and 240 or externally fitted to the center plate 150 or center pole 212 are very thin and their mechanical strengths are weak. Therefore, when they are internally fitted to the annular plates 113 and 240 or externally fitted to the center plate 150 or center pole 212, it is necessary to prevent the occurrence of damage or the like by constructing them in such a manner that the bobbins and the primary coils 180, 190, 280, and 290 are not come into contact with the annular plates 113 and 240, center plate 150, and center pole 212.
Therefore, even by any of the foregoing methods, in a state where the primary coils 180 and 280 are previously wound, their outer diameters are set to be slightly smaller than inner diameters of the annular plates 113 and 240, and the adhesive agent is filled in the gaps between the primary coils 180 and 280 and the annular plates 113 and 240 to thereby fix them. In a state where the primary coils 190 and 290 are previously wound, their inner diameters are set to be slightly larger than outer diameter of the center plate 150 or center pole 212, and the adhesive agent is filled in the gap between the primary coils 190 and 290 and the center plate 150 or center pole 212 to thereby fix them.
However, since all of the annular plates 113 and 240, center plate 150, and center pole 212 are thin, there is a problem that an area of each peripheral surface is small and adhesive strengths between the primary coils 180, 190, 280, and 290 and the annular plates 113 and 240 and the center plate 150 or center pole 212 are weak.
Generally, in the inner magnetic type electromagnetic induction speaker 100 shown in FIG. 1, after the inner peripheral side primary coil 190 is fixed to the center plate 150, the center plate 150 is fixed to the magnet 120 attached to the yoke 110 in a state where it has been positioned. In the outer magnetic type electromagnetic induction speaker 200 shown in FIG. 2, after the outer peripheral side primary coil 280 is fixed to the annular plate 240, the annular plate 240 is fixed to the magnet 220 attached to the yoke 210 in a state where it has been positioned.
When the operation to fix the annular plate 240 to the magnet 220 is performed, in order to keep predetermined gap intervals of the magnetic gaps 160 and 260, a gap gauge is inserted between the outer peripheral side primary coil 180 and inner peripheral side primary coil 190 or between the outer peripheral side primary coil 280 and inner peripheral side primary coil 290 and the gap interval is adjusted so as to be constant, thereby positioning each member. If the gap gauge is come into contact with the primary coil 180, 190, 280, or 290 at the time of the positioning operation, since the adhesive strength is weak, there is a fear that the primary coil 180, 190, 280, or 290 is dropped out from the annular plates 113 and 240, center plate 150, or center pole 212.
It is an object of a speaker apparatus of the invention to solve the foregoing problems, enable a primary coil to be easily positioned, and improve an attaching strength of the primary coil.
According to Claim 1, there is provided a speaker apparatus comprising:
a magnetic circuit portion having a magnet, a yoke for which the magnet is provided, and a top plate for forming a magnetic gap together with the yoke;
at least one primary coil arranged in the magnetic gap of the magnetic circuit portion;
a diaphragm;
a secondary coil provided for the diaphragm so as to face the primary coil in the magnetic gap;
a cylindrical member in which one side locating in the magnetic gap is attached to the primary coil and which supplies a current to the primary coil; and
a positioning portion, provided for the yoke, for positioning the other side of the cylindrical member.
In the speaker apparatus according to Claim 1, there is no need to use a gap gauge in order to obtain a predetermined gap interval of the magnetic gap, and an attaching area of the primary coil increases.